The present invention relates to a disc playback system to be used in CD-ROM playback apparatus or the like and, more particularly, to a disc playback system for controlling the disc rotation velocity.
As common methods for controlling the disc rpm in conventional disc playback Systems, there are CAV (Constant Angular velocity) control under which the angular velocity is constant, CLV (Constant Linear velocity) control under which the linear velocity is constant, and further PCAV control in which the CAV control and the CLV control are combined. Since the CLV control among these-requires frequent acceleration or deceleration of the spindle motor at a time of accessing, there are various problems, such as delay of the access time, increases in the consumed power, and heat generation. Accordingly, with the recent speeding-up of the CD-ROM apparatus, the CAV control or the PCAV control has been commonly used at the time of playback of discs on which data are recorded by the CLV method.
Under the CAV control, for example in the case of CD, the error of approximately 1.2xcx9c1.4 m/s is tolerated in the linear velocity, but the value of the linear velocity is not recorded on the medium. Thus, some methods for measuring the linear velocity of an information disc containing data recorded by the CLV method, at the time of loading of the disc are suggested.
For example, in a disc playback apparatus disclosed in Japanese Examined Patent Application No.Hei-5-50074, the linear velocity of the medium is obtained by forcefully transporting the pickup from the program start position of the information disc toward the inner radius by one track and counting the playback frame synchronization signal until the program start position is detected again. Under the CAV control, several percentages of the rotation velocity due to the error in the linear velocity is finely adjusted and the control of the rotation velocity of the disc is performed at a constant velocity. When the rpm is constant (CAV) at this time, because the linear velocity is higher at the outer radium of the disc, the playback velocity of data becomes higher. However, the maximum playback velocity conforming to the performance of the data playback circuitry has already been determined and thus the rotation velocity of the disc should be set so as not to exceed this maximum playback velocity, while the quantity of data recorded on the disc varies with discs. Therefore, following control means are suggested to solve this problem.
In the disc playback system disclosed in Japanese Published Patent Application No. Hei.7-312011, a method for calculating the outermost circumference position of a disc from TOC (Table of Contents) information of a CD-ROM and controlling the rotation velocity of the disc so as to obtain the maximum velocity in the system at the outermost circumference position containing recorded data is suggested.
In another disc playback system, a method for storing the outermost circumference position which has already been accessed, and controlling the rotation velocity of the disc so as to obtain the maximum velocity in the system at the stored address is also suggested in view of the fact that there are few cases where all data on the disc are used.
As described above, to calculate the maximum velocity, in the case of CD, the standards tolerate the error of approximately 1.2xcx9c1.4 m/s in the linear velocity. In addition to this, as for the space between tracks (hereinafter referred to as track pitch), its standard value is 1.6 xcexcm while the standards accept the error in the range of 1.5xcx9c1.7 xcexcm. For reference purposes, in the case of CD-ROM, the standard value of the track pitch is 1.6 xcexcm. Therefore, by using this value, the outermost circumference radius for obtaining the maximum velocity in the system is calculated from the address information and linear velocity of the disc.
However, in this conventional disc playback system, in the case of a disc having a smaller track pitch than the standard value, the actual playback velocity at a radius of the outermost circumference position is lower than the maximum velocity in the system. On the other hand, in the case of a disc having a larger track pitch than the standard value, the actual playback velocity at a radius of the outermost circumference position is higher than the maximum velocity of the system. Thus, in the normal disc playback system, the playback velocity at the outermost circumference position should be decided using the permissible maximum track pitch, but when a disc having a smaller track pitch than the permissible maximum value is played back in this case, the maximum playback velocity of the system cannot be realized.
To be more specific, the track pitch of a CD-ROM has a range of 1.5xcx9c1.7 xcexcm according to the standards. However, because there are discs out of the standards in practice, the target reading velocity cannot be realized or the reading velocity exceeding the processing capability of the system is obtained in the case of a disc having a value which is quite different from the standard track pitch (1.6 xcexcm).
The present invention is made to solve the above-mentioned problems, and has its object to provide a disc playback system in which the maximum playback velocity of the system can be obtained even in the case of the disc having a different track pitch.
To solve these problems, a disc playback system of Claim 1 of the present invention comprises: a pickup for reading first information data recorded on an information disc on which data are recorded at a constant linear velocity, from the information disc; a disc motor for rotating the information disc; a digital signal processing circuit for digitizing the first information data according to a playback format of the information disc; an interface control circuit for transmitting second information data which are the data digitized by the digital signal processing circuit, to an external device; a buffer memory for temporarily containing the second information data which are requested by the external device via the interface control circuit; a linear velocity detection means for detecting a linear velocity of the information disc; and a track pitch detection means for detecting a track pitch of the information disc, and this disc playback system decides a reference value for controlling a velocity of the disc motor, on the basis of the linear velocity detected by the linear velocity detection means, the track pitch detected by the track pitch detection means, and a value of a maximum radius of a record area of data which are recorded on the information disc. Therefore, the accurate values of the linear velocity and track pitch can be obtained for each disc. Accordingly, the accurate rotation velocity of the disc motor can be calculated from the values of the linear velocity and track pitch and the address value of the maximum radius of the record area of data which are recorded on the information disc, whereby the high-speed search or high-speed reading can be performed adaptively according to the outermost circumference radius of the data record area.
According to a disc playback system of Claim 2 of the present invention, in the disc playback system of Claim 1, the track pitch detection means comprises a motion distance detection means for detecting a motion distance of the pickup, and when the information disc is loaded, the motion distance detection means calculates the number of tracks which have been passed by the pickup while the pickup is moving on the data record area on the information disc for a prescribed time period or by a prescribed distance, thereby detecting the track pitch of the information disc. Therefore, the accurate value of the track pitch can be obtained fur each disc. In addition, the accurate rotation velocity of the disc motor can be calculated from the value of the track pitch, the value of the linear velocity, and the address value of the maximum radius of the record area of data which are recorded on the information disc, whereby the high-speed search or high-speed reading can be performed adaptively according to the outermost circumference radius of the data record area.
A disc playback system according to Claim 3 of the present invention comprises: a pickup for reading first information data recorded on an information disc on which data are recorded at a constant linear velocity, from the information disc; a disc motor for rotating the information disc; a digital signal processing circuit for digitizing the first information data according to a playback format of the information disc; an interface control circuit for transmitting second information data as data which have been digitized by the digital signal processing circuit, to an external device; a buffer memory for temporarily containing the second information data which are requested by the external device via the interface control circuit; a linear velocity detection means for detecting a linear velocity of the information disc; and a playback velocity detection means for detecting a playback velocity of the information disc during playback of the information, and this disc playback system previously decides an initial value of a reference value for controlling a velocity of the disc motor on the basis of the linear velocity detected by the linear velocity detection means, a standard maximum value of a track pitch of the information disc, and a value of the maximum radius of a record area of data which are recorded on the information disc, when data are read from the information disc, sets again the reference value for controlling the velocity of the disc motor adaptively on the basis of the playback velocity of the information disc during playback, which is detected by the playback velocity detection means, the linear velocity detected by the linear velocity detection means, and a value of an address at which the playback is being performed, and decides the reference value for controlling the velocity of the disc motor. Therefore, no specific means for detecting the track pitch is required, and the value of the maximum radius of a record area of data which are recorded on the information disc can be calculated less expensively and more accurately, regardless of the values of the linear velocity and track pitch of the information disc. In addition, even when the previously measured linear velocity of the information disc has an error, the high-speed search or high-speed reading can be performed adaptively according to the outermost circumference radius of the data record area.
According to a disc playback system of Claim 4 of the present invention, in the disc playback system of Claim 3, the reference value for controlling the velocity of the disc motor is obtained when the reference value for the velocity control is set again, by making a compensation by multiplying the initial value of the motor velocity control reference value, by a compensation coefficient corresponding to a ratio between a radius position at which the information disc is being played back or an address value thereof, and the value of the maximum radius of the data record area or an address value thereof. Therefore, the maximum radius of the data record area on the information disc can be calculated more accurately, by making a compensation by multiplying a compensation coefficient corresponding to the radius position where the playback is being performed or its address value, regardless of the radius position where the information disc is being played back or its address value, or the values of the linear velocity and track pitch of the disc, as well as even when the previously measured linear velocity of the disc has an error, the high-speed search or high-speed reading can be performed adaptively according to the outermost circumference radius of the data record area.
According to a disc playback system of Claim 5 of the present invention, the disc playback system of any of Claims 1, 3 and 4 extracts address information concerning the information disc which is stored in a disc start position, from the first information data, and uses a value of a radius in a maximum circumference position obtained by the address information, as the value of the maximum radius of the record area of data which are recorded on the information disc. Therefore, the maximum radius of the data record area on the information disc can be calculated more accurately, regardless of the values of the linear velocity and track pitch of the information disc, whereby the high-speed search or high-speed reading can be performed adaptively according to the data storage capacity of the disc.
According to a disc playback system of Claim 6 of the present invention, the disc playback system of any of Claims 1, 3 and 4 comprises a storage means for containing address information of the outermost circumference among already read address information on the information disc, and uses a radius of an address position of the outermost circumference, read from the storage means, as the value of the maximum radius of the record area of data which are recorded on the information disc. Therefore, the outermost circumference radius of the addresses which have ever been accessed on the information disc can be calculated more accurately, regardless of the values of the linear velocity and track pitch of the information disc, whereby the high-speed search or high-speed reading can be performed adaptively according to the address of the outermost circumference radius which has ever been accessed on the information disc.
According to a disc playback system of Claim 7 of the present invention, in the disc playback system of any of Claims 1 to 6, the disc motor comprises: a CAV (Constant Angular Velocity) control circuit for rotating the information disc at a constant angular velocity. Therefore, the maximum radius of the data record area on the disc can be calculated more accurately, regardless of the values of the linear velocity and track pitch of the disc, whereby the high-speed search or high-speed reading can be performed adaptively according to the outermost circumference radius of the data record area.
According to a disc playback system of Claim 8 of the present invention, in the disc playback system of any of Claims 1 to 6, the disc motor comprises; a CLV (Constant Linear Velocity) control circuit for rotating the information disc at a constant linear velocity, and a variable clock generation circuit which can vary a comparison clock supplied to the CLV control circuit on the basis of the reference value for controlling the velocity of the disc motor. Therefore, the maximum radius of the data record area on the information disc can be calculated more accurately, regardless of the value of the track pitch, whereby the high-speed search or high-speed reading can be performed adaptively according to the outermost circumference radius of the data record area.
According to a disc playback system of Claim 9 of the present invention, in the disc playback system of any of Claims 1 to 6, the disc motor comprises: a first rotation control means for rotating the information disc at a constant angular velocity, a second rotation control means for rotating the information disc at a constant linear velocity, and a switch circuit for switching the first rotation control means and the second rotation control means. Therefore, the maximum radius of the data record area on the information disc can be calculated more accurately, regardless of the value of the track pitch, whereby the high-speed search or high-speed reading can be performed adaptively according to the outermost circumference radius of the data record area.